Principle
QIAGEN resin is a macroporous silica-based resin with a high density of diethylaminoethyl (DEAE) groups that was developed exclusively for isolation of nucleic acids. Purification on QIAGEN resin is based on the interaction between negatively charged phosphates of the nucleic acid backbone and positively charged DEAE groups on the surface of the resin (see figure Binding principle of QIAGEN resin). The salt concentration and pH conditions of the buffers used in each step control binding, wash stringency, and elution of nucleic acids.

ApplicationsQIAGEN anion-exchange resin yields DNA or RNA of a purity and biological activity equivalent to at least two rounds of purification in CsCl gradients, in a fraction of the time. Purified nucleic acids are of the highest possible quality and are highly suitable for sensitive downstream biological applications, such as transfection, microinjection, sequencing, and gene therapy research.

Advantages
QIAGEN resin works effectively over a wide range of pH conditions (pH 6–9) and/or salt concentrations (0.1–1.6 M). This property optimizes the separation of nucleic acids — highly negatively charged, linear polyanions — from other substances and provides the highest possible nucleic acid quality. It also allows the separation of different classes of nucleic acids from one another by step elution using simple, pH and salt optimized buffers.

In contrast, conventional anion-exchangers (based on cellulose, dextran, or agarose) were developed for purification of proteins — which are generally globular and irregular in their physico-chemical properties — using varying salt concentration only. Furthermore, salt concentrations that can be used for separation with these resins range only between 0.1 M and 0.6 M due to their lower charge densities (see figures Separation of nucleic acids at neutral pH on anion-exchange resins and Comparison of structure of QIAGEN and polysaccharide-based anion-exchange resins). Under these conditions, the elution range of proteins, RNA, and DNA overlap extensively, making satisfactory separation impossible. Purification technologies such as gel filtration cannot discriminate between molecules of similar molecular weight, while products based solely on glass powder or silica gel cannot provide the degree of purity obtained with QIAGEN resin.

HiSpeed Midi Tips, provided in the HiSpeed Plasmid Midi Kit, contain a newly developed anion-exchange resin. The resin has a higher capacity, allowing higher yields of high-copy plasmid DNA to be obtained from HiSpeed Midi Tips than from classic midi tips. Furthermore, HiSpeed Tips are designed to permit a higher flow rate, allowing DNA binding, washing, and elution steps to proceed faster.

Principle QIAGEN Plasmid Plus technology delivers the same performance and quality as anion-exchange technology. QIAGEN Plasmid Plus Kits provide a novel patent-pending method for extremely fast and easy large-scale preparation of transfecton-grade plasmid DNA. The procedure can be performed in 20 (Midi and Maxi), 40 (Mega), or 50 minutes (Giga) using a vacuum and centrifuge. Optimized high-yield protocols and extra buffer volumes are provided with the kit, enabling yields from 250 μg (Midi) to 10 mg (Giga). The design and unique binding chemistry of the QIAGEN Plasmid Plus spin columns allow a simple bind-wash-elute procedure based on a novel chemistry. The resulting highly concentrated DNA is ready for immediate use in subsequent applications. For preparation of transfection-grade plasmid DNA in 96-well format, QIAGEN Plasmid Plus 96 Miniprep and BioRobot Kits are available. Samples can be conveniently processed using the QIAvac 96 and/or a centrifuge or automated on the BioRobot Universal System. Due to the proprietary binding chemistry, up to 50 μg of transfection-grade plasmid DNA per well can be obtained from up to 5 ml of an E. coli culture. The innovative binding buffer included in kits ensures very specific binding conditions, providing DNA quality that is comparable to anion-exchange preps.

Principle QIAGEN has developed a wide range of silica gel membrane products that selectively bind either RNA or DNA and separate nucleic acids within certain size parameters. A variety of modified silica gel surfaces and optimized binding buffers are used to obtain maximum discrimination between nucleic acids during adsorption and washing steps. Silica gel membranes are particularly well-suited for use in spin columns or multiwell units designed for high-throughput procedures.

Procedure Purification using QIAGEN silica gel membrane technology is based on a simple bind-wash-elute procedure. Nucleic acids are adsorbed to the silica gel membrane in the presence of chaotropic salts, which remove water from hydrated molecules in solution. Polysaccharides and proteins do not adsorb and are removed. After a wash step, pure nucleic acids are eluted under low- or no-salt conditions in small volumes, ready for immediate use without further concentration.

Advantages
Purification of nucleic acids with silica gel membrane products is fast, convenient, and economical. With QIAGEN silica gel membrane purification, there are no time-consuming phenol-chloroform extractions, or alcohol or PEG precipitations. QIAGEN silica gel membrane technology also avoids the handling inconveniences of loose silica resins or slurries and the problem of silica carryover which can interfere with downstream applications. The quality of silica gel membranes used in QIAGEN products ensures consistent yields of high-purity nucleic acids.

Principle The use of magnetic particles allows a rapid purification procedure to be performed, from the initial binding of target molecules (e.g., genomic DNA) to the particles, through to washing of the particles and elution of pure target molecules.

Procedure Purification using QIAGEN magnetic particle technology is based on a simple bind-wash-elute procedure. Nucleic acids are isolated from lysates through binding to the magnetic particles in the presence of a chaotropic salt, which removes water from hydrated molecules in solution. The particles are separated from the lysates using a magnet. The nucleic acids are then efficiently washed and eluted under low- or no-salt conditions in small volumes of elution buffer.